Constant voltage and phase network



June 26, 1962 w. H. COOK CONSTANT VOLTAGE AND PHASE NETWORK Filed Nov. 17, 1959 INVENTOR M ILBERT H Cook BY f ATTORNEYS United States Patent 3,041,527 CONSTANT VOLTAGE AND PHASE NETWORK Wilbert H. Cook, Littleton, Mass, assignor to McElroy Electronics Corporation, Littleton, Mass., a corporation of Massachusetts Filed Nov. 17, 1959, Ser. No. 853,606 Claims. (Cl. 32345) The present invention relates to voltage regulators, and more particularly, to a voltage regulator for maintaining an A.C. out-put voltage constant in response to wide variations in the amplitude of the A.C. voltage applied thereto.

In the prior art, numerous alternating current, constant voltage coupling networks have been provided for maintaining an alternating current output voltage constant in spite of wide variations in the amplitude of the input voltage. Such networks take many forms and the type of network with which the present invention is particularly concerned employs temperature-variable resistances. In networks of this general type, it is conventional to connect one or more temperature-variable resistances in series or in series and parallel with a communication network so that in response to an increase in voltage applied to the network, the impedance of the resistors increases so as to minimize the current developed in the system in response to such voltage increases. For instance, a resistor having a positive temperature coefficient of resistance may be connected in series with a non-temperature sensitive resistance so as to provide a variable voltage divider with the output current or voltage being taken across the fixed resistor. As the voltage applied to the circuit increases, the impedance of the temperature variable resistance increases so as to increase the proportion of the input voltage appearing across the variable resistor in an attempt to maintain the voltage appearing across the fixed resistor constant. Such compensating networks do not prevent a rise in the output voltage of this circuit with a rise in input voltage but do impart a drooping characteristic to the output voltage so that the output voltage versus input voltage function is nonlinear or generally exponential.

In an effort to provide better control, systems have been devised employing a temperature sensitive resistor and a transformer. At least a portion of the current flowing in the series resistive circuit also flows through a primary winding of the transformer which has a secondary winding connected in the series resistive circuit so as to introduce a bucking current in phase opposition to the current flowing through the primary winding. As the current through the resistive circuit increases, the amount of bucking current introduced into the resistive circuit by theprimary winding is increased and furthertends to linearize the operation of the circuit. Although this circuit provided an improvement over the characteristics of the circuit relying entirely upon temperature sensitive resistors, it produced an output voltage versus input voltage curve having a fiat, generally parabolic characteristic. A second difliculty in such a circuit is that the leakage reactance of the transformer introduced a phase shift into the circuit and the amount of phase shift varied with variations in the value of the temperature sensitive resistance. In consequence, a variable phase shift was introduced into any information being transmitted through the circuit and in many applications, such distortion is completely unacceptable particularly where phase in-" formation is of the essence of the information being trans "mitted. It is a primary object of the present invention to provide a constant voltage circuit which maintains an alter-- nating current output voltage constant in spite of large variations in alternating input voltage and further which ice compensates for variations in phase introduced by a transformer element employed in the circuit. I

It is another object of the present invention to provide a constant voltage circuit for maintaining an alternating input voltage to a communication circuit constant over variations in input voltage of from five to fifty volts and further to compensate for phase variations introduced by a transformer element employed in the circuit.

In accordance with the present invention, two temperature sensitive resistors or a single tapped temperature sensitive resistance is connected in series with a parallel circuit including a fixed resistor and a secondary winding of a bucking transformer. The transformer has a pri mary winding connected in parallel with one of the two temperature sensitive resistors or connected across the tapped portion of a single temperature sensitive resistor. The temperature sensitive resistors operate in the manner described with respect to the prior art in that as the input voltage increases, the resistance of the temperature sensitive resistors increase so that a smaller portion of the input voltage appears across the fixed resistor across which the output signal is taken. Such a circuit does not compensate entirely .for variations in input voltage and therefore, a transformer arrangement is employed.

In the arrangement of the present invention, the primary winding of the transformer is connected in parallel with one of the temperature sensitive resistors or across only a portion of the total temperature sensitive resistance in the circuit. As the impedance of the temperature sensitive resist-or increases with an increase in input voltage,

increase in this voltage is provided in the apparatus of the present invention by connecting the primary winding across the temperature sensitive resistance which increases the voltage drop thereacross in greater proportion.

than the increase in applied voltage. As a result of this connection of the transformer primary in parallel with the temperature sensitive resistance, a circuit is provided in which the output voltage is maintained substantially constant over variations in input voltage of from five to.

The ability to compensatefor phase variations which would normally be introduced as a result of the leakage reactance of the transformer is compensated for by con meeting the transformer in parallel with only a portion of the temperature sensitive resistance in the-circuit. Considering the equivalent circuit of a transformer, the leakage reactance of the transformer is considered to be in series with the circuit through the transformer to the secondary winding. When the voltage applied to the circuit is low and the temperature sensitive resistance is at a minimum value, the amount of current flowing through the primary winding to the secondary is quite small, and therefore the component of total current in the circuit,

which'is subjected to a phase shift by the leakage re In the prior. art circuits, as the input voltage to the circuit is increased and the impedance of the temperature sensitive resistors. increases,the proportion of the total current flowing through the transformer primary winding to the secondary winding is greatly increased so that the total proportion of the current subjected to the phase shift by the leakage; In consequence,

actance of the transformer, is quite small.

reactance of the transformer increases. the phase shift introduced into the circuit varies with the input voltage, and in systems where it is necessary to maintain the phase information of the signals such a system would normally be unacceptable. This phase shift is compensated for in the present invention by the portion of the temperature sensitive resistance which is connected in series with the primary Winding of the transformer since, as the voltage applied to the circuit increases and the proportion of the current flowing through the transformer increases, the resistance of this last mentioned temperature sensitive resistance increases thereby increasing the proportion of series resistance to the leakage reactance of the transformer. Thus, in spite of the fact that a larger portion of the current is effected by the leakage reactance of the transformer, the total phase shift in the circuit is maintained constant since the resistive component of this series current is increased. By judicious selection of the circuit parameters, the increase in the resistive component may be chosen such as to substantially counteract the increased effect of the leakage reactance at the higher voltages.

The portion of the temperature sensitive resistance in parallel with the transformer does not materially effect the phase angle of the circuit since the current subjected to phase shift by the leakage reactance of the transformer does not see the temperature sensitive resistance in parallel with the primary winding of the transformer, and consequently, the increase in the value of this resistor cannot compensate for phase changes. Therefore, it is essential to the preservation of the phase information that a portion of the temperature sensitive resistance be in series with the transformer primary winding so that variations in this resistance eifect the phase angle of the current flowing through the leakage reactance of the transformer.

It is another object of the present invention to provide a constant voltage circuit employing temperature sensitive resistors and a bucking transformer to connect a portion or the temperature sensitive resistance in series with the transformer so that as a larger portion of the current in the circuit flows through the transformer, the resistance in series with the transformer primary winding is increased as a function of the current to the primary windmg.

It is another object of the present invention to provide a circuit for maintaining substantially constant, an alternating output voltage and for compensating for phase changes in this circuit which circuit employs a relatively few, simple circuit elements in which the only active elements are temperature sensitive resistors.

The above and stii l further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein: FIGURE 1 is a circuit diagram of the present invention; and

FIGURE 2 is a graph of the output versus input voltage characteristics of the circuit under varying conditions.

Referring now specifically to FIGURES l and 2 of the accompanying drawing, there is provided an input transformer 1 having a center-tapped primary winding 2 and a secondary winding 3. The upper end of the secondary winding 3 as viewed in FIGURE 1 is connected via a series circuit comprisinga first temperature resistor 4 and a second temperature sensitive resistance 6 to one end of a secondary winding 7 of a bucking transformer 8 having a primary winding 9 connected in parallel with resistor 6. The other end of the secondary winding 7 is connected via a fixed value resistor 11 to the lower terminal of the secondary winding 3 as viewed in FIGURE 1. A resistor is connected between the lower end of winding 3 and the junction of resistor 6 and winding 7. A pair of resistors 12 and 13 have one end connected to the junction ofa secondary winding 7 and the resistor 11 and have their other ends connected to fixed contacts 14 and 16 of a switch 17 having a movable contact 18 and a further fixed contact 19. The movable contact 18 is connected to the lower end of the secondary winding 3 and is also connected to the left end of a primary winding 21 of an output transformer 22 having a center-tapped secondary winding 23. The other end of the primary winding 21 is connected to the junction of the secondary winding 7 of the transformer 8 and the resistor 11. The centertapped secondary winding 23 of the output transformer 22 and the center-tapped primary winding 2 of the input transformer 1 provide balanced input and output circuits which are particularly useful communication networks.

Zener diodes 24 and 26 are connected in series and back-to-back across the primary winding 21 of the transformer 22 so as to limit the output voltage upon the occurrence of voltage transients occurring at frequencies higher than the frequencies to which the temperature variable resistors can respond.

In the operation of the circuit, and reference is made to both FIGURES l and 2, when no voltage is applied to the primary winding 2 of the transformer 1, the output voltage is zero and therefore the graphs of FIGURE 2 start at the origin of the graph in which the input voltage is the abscissa and the output voltage is the ordinate. When voltage is applied to the primary winding 2 of the input transformer 1, current flows through the series circuit comprising resistors 4, 6, 11 and secondary winding 7 of the transformer 8 and a heating effect is developed in the resistors 4 and 6, thereby increasing their temperature and establishing an initial set of operating conditions for the purposes of explanation. The circuit of the present invention was designed to stabilize the output voltage at five volts and therefore it is assumed that the initial voltage applied to the primary winding 2 is five volts. At this point in the operation of the circuit, the resistors 4 and 6 have assumed a predetermined value, and the input voltage is divided in a predetermined ratio between the resistors 4 and 6 on the one hand and the circuit including the Winding 7, resistor 10 and resistor 11 on the other. It is assumed in this explanation that, initially, the movable contact 18 of the switch 17 is in engagement with the unconnected stationary contact 19 of the switch. With five volts applied to the input transformer, the resistor 6 assumes a predetermined value and therefore has a predetermined voltage drop thereacross which causes a current of a known value to flow through the primary winding 9 of the transformer 8. In consequence, a known value of voltage is induced in the series circuit and the combined effect of the bucking voltage and the resistors 4 and 6 stabilizes the output voltage at a predetermined value. Upon an increase of input voltage, the current flow through the circuit increases and reference is now made to the graph A of FIGURE 2 which is a plot of the compensating effect introduced only by the action of the resistors 4 and 6. As the current through the circuit increases, the resistance of the resistors 4 and 6 increases so as to increase the division ratio between the resistors 4 and 6 on the one hand and the winding 7 and the resistors 10 and 11 on the other. The graph A indicates that although the resistors 4 and 6 introduce a compensation into, the circuit which prevents the output voltage from rising in direct proportion to the input voltage, it is apparent that the compensation is insufficient to prevent a relatively large rise in the output voltage. Reference is now made to the graph B of FIGURE 2 which is a plot of the effect of the transformer 7 independently of the effect of the resistors 4 and 6 as indicated by the graph A. It is obvious that the effect of the change in value of the resistor 6 on current flow through the transformer primary.

winding cannot be ignored, but the effect of this resistor as a compensating element in the series circuit is ignored in the graph B. Upon an increase in input voltage, the" value of the resistor 6 increases and therefore there is an increase in the voltage applied across the primary winding 9 which increase is a non-linear function of the input voltage. Specifically, the voltage across the primary winding 9 rises at a greater rate than the applied voltage due to the action of the resistor 6 and the bucking voltage introduced into the secondary winding 7 increases as a non-linear function of the applied voltage.

By properly choosing the relative values of the resistors 4 and 6 and of the primary winding 9, the two curves A and B may be chosen so that the curve B has a negative slope proceeding from the five volt point which is numerically equal to the positive slope of the curve A also proceeding from the five volt point, and in consequence, an output voltage graph, graph C, is produced which is linear over the operating range of the circuit, this being from'five to fifty volts in the indicated example.

As indicated above, certain relationships must exist between the temperature sensitive resistors and the transformer. Specifically, the transformer winding 7 should be of a low resistance so as to not materially affect the division ratio between the resistors 4 and 6 on the one hand and the resistor 11 on the other. It is apparent that since the output voltage is taken across the resistor 11 alone, the winding 7, being of a fixed value of resistance, introduces a constant factor into the voltage divider. This constant factor must be kept small so that it does not materially affect the variable voltage division factor. With regard to the primary winding 9, its value must be relatively high with respect to the value of the resistance 6 since, if the resistance of the winding 9 were less than the resistance of the winding 6, variations in the value of resistor 6 would have little effect upon the division of voltage in the circuit. In a specific embodiment of the invention, the impedance as seen in circuit of the primary winding 9 is 5000 ohms while the impedance of the secondary winding 7 is 100 ohms. The resistors 4 and 6 in the example given are approximately equal in value, although this is not a limiting condition at all as will become apparent subsequently, and have values which range from approximately 200 to 800 ohms over the operating range of the circuit. With these values, it is found that the characteristic curve C as illustrated in FIGURE 2 may be obtained by the circuit of the invention. The value of the resistor 11 is not critical and only determines the level of the output voltage. The resistor 10 is employed to reduce the effects of the inductance of the winding 7 on the output voltage while the resistor 11 is employed as an impedance matching element. In some instances where impedance matching is not necessary or where the circuit, without resistor 11, is matched to the external load, the resistor 11 may be eliminated in which case the winding 7 is connected directly across the resistor 6. The resistors 12 and 13 are employed to permit a change in the specific output voltage chosen. Obviously, connecting either one of these resistors into the circuit changes the effective impedance of the circuit in series with the temperature variable resistors and therefore, changes the division ratio of the apparatus.

As previously indicated, the resistor 4 connected in series with the primary winding 9 of the transformer 8 is employed to compensate for phase variations which would otherwise occur as a result of a varying portion of the load current flowing through the leakage reactance of the primary and secondary windings of the transformer 8. If the primary winding 9 were connected in parallel with all the temperature. sensitive resistance in the circuit, then as the temperature sensitive resistance increased and a larger proportion of the current in the series circuit flowed through the transformer 8, the eflect of the leakage reactance would increase even though the absolute value of leakage inductance remained the same. Considering extreme examples, if the value of the resistance 6 were zero, then the primary winding 9 would be short circuited and the leakage inductance of the primary winding would have no effect upon the circuit and no phase shift would be introduced. On the other hand, if the value of the resistance 6 were infinite, then all of the current in the circuit would flow through the transformer 8 and all of the current would be subjected to the leakage inductance of the transformer. If nothing further were done, the change in phase angle of the current with changes in input voltage would be quite severe.

In a practical case, the extremes of resistance set forth above could not be realized. However, the effect of variation of the resistance 6 is to cause varying proportions of the total current to be subjected to the effects of the leakage inductance of the transformer, thereby tending to introduce phase shift into the circuit. In

the present invention, as the value of the resistor 6 increases, thereby increasing the proportion of the current flowing through the transformer 8, the value of the resistor 4 also increases so that as a larger proportion of the current in the circuit is subjected to the effect of the leakage reactance, the resistance through which this portion of the current flows also increases and by properly proportioning the value of the resistor 4 to the value of the leakage reactance in the circuit, the phase angle may be maintained within acceptable limits even for information conveyed as a variable phase signal.

While I have described and illustrated one specific embodiment of my invention, it will be clear that varia tions of the details of construction'which are specifically illustrated and described may be resorted to Without departing from the true spirit and scope of the invention as defined in the appended claims. i

What I claim is: l. A constant voltage circuit comprising a temperature sensitive impedance, a further impedance, a transformer,

having a primary winding and a secondary winding, means connecting said impedances and said secondary winding in a series circuit, means for applying an input voltage across said series circuit, means connecting said primary winding in parallel with at least a part of said temperature sensitive impedance, said secondary winding being connected in said series circuit such that the current induced therein by current flowing in said primary winding is in phase opposition to the current in said series circuit and an output circuit connected across said further impedance.

2. A constant voltage circuit comprising a tempera ture sensitive impedance, a further impedance, a transformer having a primary winding and a secondary winding, means connecting said impedances and said secondary winding in a series circuit, means for applying an input voltage across said series circuit, means connecting said primary winding in parallel with at least a part of said temperature sensitive impedance, said secondary winding being connected in said series circuit such that the current induced therein by current flowing in said primary winding is in phase opposition to the current in said series circuit, an output circuit connected across said further impedance and an amplitude limiter connected in said output circuit.

3. A constant voltage circuit comprising a temperature sensitive impedance, a further impedance, a transformer having a primary winding and a secondary winding, means connecting said impedances and said secondary Winding in a series circuit, means for applying an input voltage across said series circuit, means connecting said primary winding in parallel with at least a part of said temperature sensitive impedance, said secondary winding being connected in said series circuit such that the current induced therein by current flowing in said primary winding is in phase opposition to the current in said series circuit and an output circuit connected across said further impedance, said secondary winding having low impedance and said primary winding having a high impedance relative to the value of said part of said temperature sensitive impedance.

4. A constant voltage circuit comprising a temperature sensitive impedance, a further impedance, a transformer having a primary winding and a secondary winding,

7 means connecting said impedances and said secondary Winding in a series circuit, means for applying an input voltage across said series circuit, means connecting said primary Winding in parallel with said temperature sensitive impedance, said secondary winding being connected in said series circuit such that the current induced therein by current flowing in said primary winding is in phase opposition to the current in said series circuit, and an output circuit connected across said further impedance, and means for increasing the resistance of said series circuit in series with said primary winding as a function of the current therethrough.

5. A constant voltage circuit comprising a temperature sensitive impedance, a further impedance, a transformer having a primary winding and a secondary winding, means connecting said impedances, and said secondary Winding in a series circuit, means for applying an input voltage across said series circuit, means connecting said primary winding in parallel with a part only of said temperature sensitive impedance, said secondary winding being connected in said sen'es circuit such that the current induced therein by current flowing in said primary winding is in phase opposition to the current in said series circuit and an output circuit connected across said further impedance 6. A constant voltage circuit comprising a temperature sensitive impedance, a further impedance, a trans former having a primary winding and a secondary winding, means connecting said impedances and said secondary winding in a series circuit, means for applying an input voltage across said series circuit, means connecting said primary winding in parallel with a part only of said temperature sensitive impedance, said secondary winding being connected in said series circuit such that the current induced therein by current flowing in said primary winding is in phase opposition to the current in said series circuit, an output circuit connected across said further impedance, and an amplitude limiter connected in said output circuit.

7. The combination according to claim 6 further com- I 8 prising means for selectively varying the impedance of said further impedance.

8. A constant voltage circuit comprising a temperature sensitive impedance,-a further impedance, a transformer having a primary winding and a secondary winding, means connecting said impedances and said secondary winding in a series circuit, means for applying an input voltage across said series circuit, means connecting said primary winding in parallel with a part only of said temperature sensitive impedance, said secondary winding being connected in said series circuit such that the current induced therein by current flowing in said primary winding is in phase opposition to the current in said series circuit, an output transformer having a primary winding connected across said further impedance and means for limiting the maximum voltage across said primary winding.

9. A constant voltage circuit comprising a temperature sensitive impedance, a further impedance, a transformer having a primary winding and a secondary winding, means connecting said impedances and said secondary winding in a series circuit, means for applying an input voltage across said series circuit, means connecting said primary winding in parallel with said temperature sensitive impedance, said secondary winding being connected in said series circuit such that the current induced therein by current flowing in said primary winding is in phase opposition to the current in said series circuit and an output circuit connected across said further impedance.

10. The combination according to claim 9 further comprising means for selectively varying the value of said further impedance.

References Cited in the file of this patent UNITED STATES PATENTS 2,686,289 Squires Aug. 10, 1954 2,690,535 Douma Sept. 28, 1954 2,753,512 Helterline et al July 3, 1956 

